Micrographite (μG) and Polypropylene (PP) Composites: Preparation and Influence of Filler Content on Property Modifications

Abstract

It is difficult to select low-cost filler materials. Specifically, carbon-based filling materials are a matter of concern, and developing a carbon-filled polymer composite with enhanced properties is necessary. In this study, the authors developed a polymer composite using virgin polypropylene (PP) as a matrix and affordable micrographite (µG) as a filler. The developed composite has many potential applications in the automotive, aerospace, and electronic industries. To prepare the test specimens, the composite was prepared using a twin-screw extruder containing 3, 6, 9, 12, or 15 wt.% µG powder (BET surface area ≈ 29 m2/g; particle size > 50 µm) followed by injection molding. Different mechanical properties like the tensile, flexural, and impact strengths were determined. The prepared composites were further characterized by means of XRD, TGA, DSC, FTIR, DMA, FESEM, and PLM tests. The results were analyzed and compared with those for PP. Improved tensile (up to ≈ 34 MPa) and flexural (up to ≈ 40 MPa) strength was observed with an increase in the µG content. However, the impact strength continuously decreased (maximum ≈ 32 J/m for PP) with fractures. These findings underscore that graphite plays a significant role in controlling the deformation behavior and ultimate strength of composites. An XRD analysis revealed that adding graphite restructured the crystalline arrangement of PP and altered the composite’s crystallographic properties. Nonetheless, no induction effect (β-phase formation) was observed. A moderate enhancement in the thermal stability was observed owing to a small increase in the melt (Tm), onset (Tonset), and residual (TR) temperatures. A microstructural analysis showed that the micrographite powder strongly prevented spherulite growth and modified the graphite powder’s rate of dispersion and agglomeration in a polymer matrix. The results show that graphite could be a viable low-cost alternative carbon-based filler material in polypropylene matrices.